In freezing temperatures it's not uncommon for some people's windshield washer fluid to freeze. If this hasn't happened to you before, consider yourself lucky. Not being able to see out of your front window is extremely dangerous.
Choosing the Best Fluid for Prevention.
Of course, prevention is always the best option. To prevent your windshield wiper fluid from freezing make sure you buy a good quality windshield wiper fluid that is appropriate for the weather.
There are many different kinds of windshield washer fluid, from “all-season” to “de-icer,” but if you live anywhere that gets extremely cold, you're going to want to pick up a winter solution, rather than a summer one. The ratio in a winter solution is typically 1:1—1 part anti-freeze and 1 part water—whereas a summer blend is usually 1:10—1 part antifreeze and 10 parts water.
You do not want to use a summer blend in the winter, because it will have more water in it than a winter blend. You can also buy an anti-freeze windshield wiper fluid, which is typically alcohol-based; this solution will not only prevent freezing, but also melt frost and ice on your windshield.
Sometimes even the “right” fluid gets old and the methylated spirits evaporate, making your washer fluid mostly water, and we all know that water freezes rather quickly in freezing temperatures. Not to mention, cheaper washer fluids already have more water mixed in than the more expensive ones.
If your washer fluid freezes, you have to thaw it out. The important thing to remember is that if it freezes once it will freeze again. After you manage to thaw it out, you have to drain it completely and put in a better washer fluid, or you're not really fixing the problem.